Unexpected processing-induced particle/matrix interactions in magnetic composites based on thermoplastic matrix

Abstract

Understanding processing-induced changes in the polymer composites is of the utmost necessity as it affects the final properties and the reliability of the products. Despite their importance, related investigations are frequently overlooked, especially in the case of magnetorheological elastomers (MREs). In this study, the processing-induced changes were investigated within an isotropic MRE based on a thermoplastic elastomer (TPE) matrix loaded with carbonyl iron (CI) microparticles. Systematic thermomechanical tests in the molten state were used to mimic the processing conditions, revealing the time evolution of the particle/matrix interactions. The interactions manifested as an increase in the viscoelastic properties, which was attributed to the development of a secondary network composed of the confined polymer chains in the vicinity of the CI particles. The restricted mobility improved the reinforcing effect and structural integrity but diminished the field-induced stiffening of the composite, i.e., the magnetorheological effect. The existence of the particle/matrix covalent bonding was postulated and explained based on the coupling reaction between the thermomechanically-induced radicals formed in the polymer chain and the alkoxyl radicals on the surface of the CI particles. The new findings are highly relevant for the further development of reprocessable and recyclable TPE-based MREs, while the robust measuring protocol is deemed to be implementable for studying particle/matrix interactions in diverse composite systems.